Defect band enhanced Ca9Y(VO4)7: Yb3+/Er3+/Sr2+ phosphor upconversion luminescence for multimode optical temperature measurement

Abstract

This study explored the enhancement of strong red and near-infrared emissions in Ca₉Y(VO₄)₇: Yb³⁺/Er³⁺ through doping with Sr²⁺ ions under a 980 nm laser. The phosphor exhibits weak green (528 nm, ²H_11/2 → ⁴I_15/2 and 550 nm, ⁴S_3/2 → ⁴I_15/2) and red (654 nm, ⁴F_9/2 → ⁴I_15/2) emissions, alongside a strong emission in the near-infrared range (807 nm, ⁴I_9/2 → ⁴I_15/2). The optimal doping concentration of Sr²⁺ in Ca₉Y(VO₄)₇: Yb³⁺/Er³⁺ is 0.2, and the upconversion quantum yield is 4.91%. The enhancement of upconversion red and near-infrared emissions is ascribed to defect bands, playing a crucial role in facilitating the energy transfer from green levels to red and near-infrared levels. A multi-mode temperature sensor of Ca₉Y(VO₄)₇: Yb³⁺/Er³⁺/Sr²⁺ phosphor was developed, featuring three temperature sensing modes based on the luminescent intensity ratio of ⁴F_9/2/⁴I_9/2 and ²H_11/2/⁴S_3/2 thermally coupled levels, as well as the LIR of ²H_11/2/⁴F_9/2 non-thermally coupled levels. Corresponding maximum relative sensitivities were 0.85% K⁻¹ at 298 K, 1.18% K⁻¹ at 298 K and 1.21% K⁻¹ at 298 K, respectively. The phosphor demonstrates notable temperature sensitivity, highlighting its potential in optical temperature sensing. This study introduces an innovative platform for crafting multi-mode self-reference optical temperature sensors, presenting substantial advancements in the field.